http://www.jpk.pku.edu.cn/pkujpk/course/sjjg/chapter4/05/t01_jj.html
http://jpkc.ncwu.edu.cn/sjjg/new/content/ch6/ch6-2-04.htm
http://210.43.128.116/sjjg/precis/precis-0.htm
http://tomatoman.blogbus.com/logs/1541743.html
http://blog.youkuaiyun.com/lijuwen/archive/2007/06/13/1650568.aspx
http://blog.163.com/yhss_214/blog/static/1037697920070414856354/
http://www.nocow.cn/index.php/%E4%BA%8C%E5%8F%89%E6%A0%91
http://www.cnblogs.com/xiaosuo/archive/2010/02/08/1654145.html